Doktorsavhandling, 2002

This thesis presents the research and development of a microwave instrument to capture tomographic information from the inner structure of the biological sample. The principle of the instrument is based on the anisotropy introduced by the fibres in materials such as wood and muscles in terms of information regarding changes in the fibre structure. The information is presented as images representing the state of polarization using Stokes parameters, the complex polarization ratio, and the ellipticity and the linear tilt angles. The theory of wave propagation in anisotropic media is discussed and related to the dielectric properties of wood. Experiments have shown that the developed instrument can be utilized in various applications such as localizing knots and cavities in wood and to detect mechanical contamination of meat. A second instrument has been improved by introducing a new signal analysis step to estimate the relative shrinkage profile of paper. The estimator is based on tracking frequency variations in the joint time frequency spectrum and follows the lower bound of the problem for the relevant noise levels.